The field of the invention is laboratory apparatus and the invention relates more particularly to devices for concentrating small liquid specimens.
One disposable device is shown in U.S. Pat. No. 3,187,379 assigned to Amicon Corporation wherein a liquid specimen is placed in a chamber which has a membrane along one side. The membrane has an absorbent material pressed against its inner surface and the specimen is poured into a chamber against its outer surface. The specimen tends to flow through the membrane into the absorbent material. In one form, an impervious sheet is placed near the lower portion of the chamber to retain a certain minimum amount of liquid in the chamber no matter how long the sample is left in the chamber. While the Amicon device has found widespread use, it has several shortcomings. First, the time required for concentration to be completed can be quite slow, often taking up to one day. Secondly, the sample is open to the atmosphere and if left overnight, a portion of the sample can be lost. Because of the design of the Amicon device and its use of an impervious layer, the sample is in contact with only a very small amount of the membrane as it nears the level of the impervious layer.
To reduce concentration time, the centrifugation of a sample over a membrane is sometimes used to increase the flow through the membrane. Centrifugation requires additional equipment and provides limited control over final sample volume.